Benign ovarian serous cystadenoma mimicking papillary thyroid carcinoma metastasis on I-131 SPECT/CT.

Volume 95 No. 2 February 2012 CliniCal presentation A 34 year-old female patient was found on ultrasound to have multinodular goiter with a complex 1.3 cm thyroid nodule in the lower pole of the left thyroid lobe. Fine needle aspiration of this thyroid nodule revealed cytology that was highly suspicious for cystic papillary thyroid carcinoma. She underwent total thyroidectomy; surgical pathology showed an eight mm and a second seven mm papillary carcinoma within this nodule with negative margins. She was started on levothyroxine after thyroidectomy. A thyrogen-stimulated diagnostic I-131 scan (Figure 1) showed a single focus of increased uptake in the mid thyroid bed consistent with residual thyroid tissue or tumor, with a 52-hour uptake of 0.4% without evidence of additional sites of metastatic disease. A rounded focus of activity in the mid pelvis was presumed to represent normal bladder activity. She was treated with 149.7 mCi of I-131. Post-treatment thyroid scan (Figure 2) at seven days showed a small amount of activity in the thyroid bed and a large focus of intense activity in the lower pelvis that was thought to represent a distended bladder, but which was more prominent compared to the diagnostic study. Straight catheterization of the bladder was performed to decrease the radiation to the bladder. However, this large focus of activity (Figure 3) persisted after emptying the bladder by straight catheterization. SPECT/CT scan of the pelvis (Figure 4) showed increased uptake within a large mass immediately anterior to the uterus, with the bladder decompressed. The patient reported that she had a prior ultrasound performed at an outside institution that showed a large mass arising from her left ovary, which raised the possibility of a large struma ovarii. She underwent left salpingo-oophorectomy and pathology revealed a diagnosis of benign serous cystadenoma of the ovary Benign ovarian serous cystadenoma mimicking Papillary thyroid carcinoma metastasis on i-131 sPect/ct